Sania Mirza [Images] registered her second big upset in successive days as she packed off fourth-seeded Patty Schnyder of Switzerland [Images] in straight sets to storm into the semi-finals of the US $600,000 Bank of the West of Classic.

Unseeded Sania beat Schnyder 7-6 (7/2), 6-1 and set up a semi-final clash with eighth seed Austrian Sybille Bammer.

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Bammer advanced with a 6-2, 6-1 victory over wild card Lilia Osterloh of the United States.

Sania had accounted for sixth-seeded Tatiana Golovin [Images] of France [Images] for a place in the quarter-finals.

World No 17 and last year finalist Schnyder got off the blocks in a flash and raced to a commanding 5-2 lead before Sania came back hitting some powerful strokes and pushed the set to a tie-break, which she pocketed 7-2.

Cheered on by a big crowd, the Indian ace was in full flow in the second set and disposed of Schnyder for th loss of just one game.

"Experience and maturity are two things that I have learnt over the last two years and it helped out tonight," said Sania, who reached the semi-finals at Cincinnati last week.

"When I am on the court, the crowd does get me going. This crowd is always cheering and there is always a positive vibe. But at the end of the day, you are the player and you are down 5-2, so you have to get it done," Sania said.

Sania, however, said beating two players ranked in the top-20 does not mean that she is going to take her semi-final opponent, Sybille, whom she has never played before, lightly.

"Just because I was able to beat Golovin and Schnyder does not mean the road gets any easier tomorrow. Sybille is a great player and she is in the semi-finals so she has been doing things right too.

"She [Sybille] has also been to a final this year. The only advantage maybe is that I played a left-hander today and now I will be playing another left-hander tomorrow," said the world No 35.

In the other semi-final, top-seeded Russian Anna Chakvetadze [Images] will take on third-seeded Slovakian Daniela Hantuchova [Images].

Chakvetadze rallied to beat seventh-seeded Katarina Srebotnik of Slovenia 4-6, 6-2, 6-2 while Hantuchova advanced with a 7-5, 6-3 victory against qualifier Olga Govortsova of Belarus.

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